Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates

Fischer, Sarah C. L.; Arzt, Eduard; Hensel, René

doi:10.1021/acsami.6b11642

Cited by 80 publications

(69 citation statements)

References 48 publications

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“…The design parameters investigated were the thickness of the soft tip layer, the ratio of the elastic moduli, and the curvature of the interface between the two materials ( Figure ). The pull‐off strength values were predicted to increase for thinner layers and larger modulus ratios in accordance with experimental results on model structures (Figure a) . For all elastic modulus ratios, a thinner layer resulted in a decreased magnitude of the edge stress singularity, whereas the stress at the center was increased related to a “confinement” effect .…”

Section: Principles Of Adhesive Micropatternssupporting

confidence: 84%

“…Furthermore, the increment of the energy release rate during detachment varied with the extent of confinement. This means that with decreasing film thickness (i.e., larger degree of confinement), the detachment mechanism changes from unstable growth of edge cracks to more stable growth of finger‐like or center cracks . It should be noted that the effect due to confinement of the soft terminal layer depends strongly on material compressibility (i.e., Poisson's ratio) .…”

Section: Principles Of Adhesive Micropatternsmentioning

confidence: 99%

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Engineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications

Hensel

Moh

Arzt

2018

Adv Funct Materials

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142

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Reversible adhesion is the key functionality to grip, place, and release objects nondestructively. Inspired by nature, micropatterned dry adhesives are promising candidates for this purpose and have attracted the attention of research groups worldwide. Their enhanced adhesion compared to nonpatterned surfaces is frequently demonstrated. An important conclusion is that the contact mechanics involved is at least as important as the surface energy and chemistry. In this paper, the roles of the contact geometry and mechanical properties are reviewed. With a focus on applications, the effects of substrate roughness and of temperature variations, and the long-term performance of micropatterned adhesives are discussed. The paper provides a link between the current, detailed understanding of micropatterned adhesives and emerging applications. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201800865.are designated for locomotion over various types of substrates, involving attachment and detachment within milliseconds. [1][2][3][4][5] It is of interest for evolutionary biologists that many foot pads are strikingly similar in morphology: elongated fibrillar structures with aspect ratios ranging from 10 to 80 leading to terminal elements with very different shapes (Figure 1a and Figure 3). [6][7][8][9] For some animals such as the gecko, the adhesive ability of their toe pads can be attributed to van der Waals interactions and, to some extent, to capillary forces. [10][11][12][13][14][15] In the gecko, the fibrillar pads are composed of millions of keratinous hairs (called setae) that branch into even finer terminal elements (spatulae) (Figure 1a). [16,17] Such a hierarchically organized structure results in a soft and compliant surface, which allows easy adaption to roughness at the expense of little strain energy and thus enhances adhesion.More than 1000 reports published in the field of bioinspired dry adhesives over the last two decades reflect a considerable interest in resolving the underlying adhesion mechanisms, e.g., refs. [18][19][20][21]. Application-oriented publications were motivated by a strong interest in creating novel gripper devices and pickand-place systems (Figure 1b), e.g., refs. [18-20] and [22][23][24], climbing robots for terrestrial and extraterrestrial activities, [25][26][27][28][29][30][31][32] new gasket designs in microfluidics, [33,34] or novel solutions for biomedical applications. [35][36][37][38] The present feature article aims to describe the path from fundamental considerations, including a detailed understanding of the relevant contact mechanics, to emerging applications. It is now known that the success of mimicking micropatterned dry adhesives critically depends on the interplay between design parameters, such as dimensions of the structure elements and the terminal tip-shape geometry, and the bulk and surface properties of the materials in contact. How these parameters control the adhesive performance of synthetic...

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Section: Principles Of Adhesive Micropatternssupporting

confidence: 84%

Section: Principles Of Adhesive Micropatternsmentioning

confidence: 99%

Engineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications

Hensel

Moh

Arzt

2018

Adv Funct Materials

Self Cite

142

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“…Inspired by the unique properties of adhesive surfaces found in nature, micropatterned adhesives are currently under intense research for handling fragile and miniaturized objects, even in demanding environments such as vacuum . Among the various designs, microstructures with mushroom‐shaped tips have an exceptionally high adhesion . It was demonstrated that their pull‐off force, i.e., the force necessary for detaching the adhesive from a substrate, was up to an order of magnitude higher than with nonoptimized flat punch pillars .…”

Section: Introductionmentioning

confidence: 99%

In Situ Observation Reveals Local Detachment Mechanisms and Suction Effects in Micropatterned Adhesives

Tinnemann

Hernández

Fischer

et al. 2019

Adv Funct Materials

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Fibrillar adhesion pads of insects and geckoes have inspired the design of highperformance adhesives enabling a new generation of handling devices. Despite much progress over the last decade, the current understanding of these adhesives is limited to single contact pillars and the behavior of whole arrays is largely unexplored. In the study reported here, a novel approach is taken to gain insight into the detachment mechanisms of whole micropatterned arrays. Individual contacts are imaged by frustrated total internal reflection, allowing in situ observation of contact formation and separation during adhesion tests. The detachment of arrays is found to be governed by the distributed adhesion strength of individual pillars, but no collaborative effect mediated by elastic interactions can be detected. At the maximal force, about 30% of the mushroom structures are already detached. The adhesive forces decrease with reduced air pressure by 20% for the smooth and by 6% for the rough specimen. These contributions are attributed to a suction effect, whose strength depends critically on interfacial defects controlling the sealing quality of the contact. This dominates the detachment process and the resulting adhesion strength.

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“…Since developing an understanding of the underlying principles of fibrillar adhesive systems in nature, careful attention has been paid to the design and fabrication of synthetic fibrils for both strength and reversibility . Efforts addressing the former have primarily focused on controlling the fibril‐substrate interfacial stress distribution through modification of the tip geometry.…”

Section: Introductionmentioning

confidence: 99%

Benefit of Backing‐Layer Compliance in Fibrillar Adhesive Patches—Resistance to Peel Propagation in the Presence of Interfacial Misalignment

Booth

Bacca

McMeeking

et al. 2018

Adv Materials Inter

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Investigations of backing‐layer effects in bioinspired fibrillar adhesives have shown that increased compliance is detrimental to the strength of fibril arrays under normal loading due to an increase in severity of a circumferential load concentration. In this work, the impact of misalignment on the performance of fibrillar adhesive patches contacting smooth flat surfaces is examined, demonstrating that the conditions for circumferential detachment are extremely limited. For an array of fibrils on a backing layer of varying thickness, normal adhesion tests are performed against a flat surface that maintains a fixed angle of misalignment with respect to the adhesive surface. In the aligned state the detachment is circumferential and the detachment force is highest for the thinnest, least compliant backing layer. However, for misalignment angles on the order of just 0.1°, peel‐like detachments are observed. The thickest backing layer, being 210% more compliant than the thinnest, yields a 43% increase in the adhesive strength at a misalignment angle of 0.4°. This suggests that out‐with conditions of precise alignment, backing‐layer compliance is beneficial to strength under normal loading. A mechanical model is presented, revealing the mechanism behind enhanced resistance to peel propagation is deformation of the backing layer at the detachment front which reduces differential stretching of fibrils.

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Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates

Cited by 80 publications

References 48 publications

Engineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications

Engineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications

In Situ Observation Reveals Local Detachment Mechanisms and Suction Effects in Micropatterned Adhesives

Benefit of Backing‐Layer Compliance in Fibrillar Adhesive Patches—Resistance to Peel Propagation in the Presence of Interfacial Misalignment

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